1. Field of the Invention
This invention relates to a pattern generator, and more particularly to improvements in a method of making or trimming a pattern with a pattern generator.
2. Description of the Prior Art
A pattern generator having hitherto been used employs a method in which a shaped pattern is projected on a photosensitive material (photoresist) and in which a large number of such shaped patterns are used to form an enlarged pattern (hereinbelow, called the "reticle pattern" and generally termed the "reticle") which is at least 5 times larger than an IC chip pattern.
FIG. 1 shows a schematic view of the pattern generator having heretofore been used. Light emerges from a light source 1, and a light beam having a specified wavelength is projected onto a photoresist film applied on the surface of a workpiece (reticle substrate) 8, by an optical unit 2 which is composed of a shutter, filter, lens etc. and through a reduction projection lens system 7 which has a reduction ratio of at least 5. That is, an enlarged shaped pattern formed by slit assemblies composed of parts 3, 3' and 4, 4' which are disposed between the optical unit 2 and the reduction projection lens system 7 (for example, in case where a reticle being 10 times larger is fabricated and where a 1/10-reduction projection lens is used, the enlarged shaped pattern is 100 times larger than the actual size) is reduced and projected to form a resist latent image pattern. In order to obtain a desired enlarged shaped pattern, gears 5 and 6 are driven with control signals delivered from a data processing system (not shown), to widen or narrow the interspaces of the slit assemblies 3, 3' and 4,4' and thus control the size of a slit opening. Further, an X-direction stage 11 and a Y-direction stage 12 which hold the recticle substrate 8 are controlled by the data processing system, to relatively move the enlarged shaped pattern to a desired position on the recticle substrate 8, whereupon the reduced image of the enlarged shaped pattern is made. In such way, resist latent image patterns in any desired arrayal are formed. In the figure, numeral 13 indiates a base, and numerals 14 and 15 indicate motors for driving the X-direction stage and Y-direction stage, respectively.
As explained above, the reticle fabrication by the prior-art apparatus adopts wholly the mechanical drive system such as the mechanical drive of the slit assemblies for controlling the size of the enlarged shaped pattern and the mechanical drive of the stages for controlling the arrayal of the enlarged shaped patterns. Therefore, it poses problems in points of the fabrication time and the fabrication precision. Especially as to the fabrication time, it is the present situation that a long period of time of about 10 hours is required for fabricating an ordinary LSI pattern.
On the other hand, since the reticle pattern formed by the prior-art pattern generator illustrated in FIG. 1 is the resist latent image pattern, processing steps such as the formation (developing) of a resist pattern and the etching of a shading material are further required after the exposure. FIGS. 2a-2i constitute a flow chart showing an example of a process for fabricating the reticle pattern. First, as shown in FIG. 2a, using a thermal beam 16, a sample (reticle substrate) 8 in which a shading material 9 is deposited on a transparent glass substrate 10 is subjected to baking prior to coating with a resist. Subsequently, as shown in FIG. 2b, whilst rotating the sample 8, the resist material is dropt thereonto so as to form a uniform resist film 17 on the shading material 9. Thereafter, as shown in FIG. 2c, the sample 8 is prebaked with the thermal beam 16 again. Thereafter, upon confirming that the temperature of the sample has lowered to the room temperature, the resist latent image 18 of a desired pattern is formed as shown in FIG. 2d by the use of the pattern generator explained with reference to FIG. 1. Subsequently, as shown in FIG. 2e, the resist latent image pattern formed by the pattern generator is treated with a resist developer 19, thereby to develop the resist pattern 17. Thereafter, the developed pattern is fixed with a rinse, and the resultant sample is post-baked with the thermal beam 16 as shown in FIG. 2f. Subsequently, as shown in FIG. 2g, using the resist pattern 17 as a mask, the shading material 9 is chemically etched with an etchant 20 so as to form the pattern of the shading material 9. After the etching, the sample is washed with water, and the resist pattern 17 is removed with a resist stripper 21 as shown in FIG. 2h. Lastly, the resultant sample is washed with water and dried. Then, the fabrication of the reticle made up of the shading material pattern 9 and the glass substrate 10 as shown in FIG. 2a is finished.
As described above, the prior-art process has the disadvantage that large numbers of thermal treatment and chemical treatment steps are necessitated. In particular, the reticle fabricating steps other than the foregoing step of forming the resist latent image pattern take a long period of wasteful time. As the period of time for the series of thermal and chemical treatments, at least 2 hours are required. Along with shortening of the period of time for the formation of the resist latent image pattern itself, improvements in or omission of such attendant processing steps have/has become an important subject.